The present invention relates generally to water treatment, and more in particular to the removal of organic contaminants from water.
In the operation of many industrial processes, large quantities of effluent water are produced. Such water often contains organic materials dissolved therein as undesirable contaminants. Removal of these organic materials has posed a problem for industry, particularly when the objectionable organic materials have lower pure component vapor pressures and higher boiling points than water.
One approach to removing organic contaminants from water has been to vaporize and expel the volatile contaminants from the water by contacting the contaminants with a stripping vapor such as, for example, steam, natural gas, or air. Typical processes of the above types are taught, for example, in U.S. Pat. Nos. 2,141,349; 2,527,444; 2,773,003; 2,927,075; 2,930,753; and by L. J. Thibodeaux in "Air Stripping of Organics from Wastewater: A Compendium", proc. 2nd Nat'l. Conf. on Complete WateReuse: Water's Interface With Energy, Air, and Solids, AIChE, N.Y. (1975).
Contaminants that can be removed by such conventional processes are generally limited to low molecular weight compounds having higher pure component vapor pressures at 25.degree. C. than water and lower normal boiling points than water (one atmosphere pressure). Such contaminants are known to be more volatile than water, and are expected form thermodynamic considerations to be readily desorbed into a stripping vapor.
A process employing air as the stripping vapor is discussed by Thibodeaux. Thibodeaux suggests that some organic contaminants which exhibit a lower pure component vapor pressure at 25.degree. C. than water and a higher normal boiling point than water can be vaporized into an air stream if the activity coefficient of the contaminant in water is sufficiently large. However, an examination of the vapor-liquid equilibria data presented by Thibodeaux at page 362 demonstrates that even with large activity coefficients, organic contaminants having a normal boiling point in excess of 181.4.degree. C. (Thibodeaux, Table 1), are not expected to be susceptible to vaporization be a stripping vapor due to their low relative volatilities.
However, in many applications, it is necessary to remove from water organic contaminants having lower pure component vapor pressures at 25.degree. C. than water and having normal boiling points in excess of 200.degree. C. It is thus desirble to develop a simple process for removing such contaminants from water which is effective, energy efficient, and economically attractive.